LOCAL INCIDENCE IN MILK EPIDEMICS 



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nature of a collection of signs and characteristics which have, up to 

 the present, been observed in milk-borne disease. For convenience 

 we shall state them briefly and in some sort of tabular form : — 



1. Special incidences of disease when conveyed by milk 



(a) Local Incidence. — Milk-bome infection follows the milk cart. 

 — In almost every epidemic traceable to milk on record, as far as 

 we know, the conveyed disease has appeared in the main along 

 the lines of distribution. In some cases outbreaks have followed 

 with remarkable precision the exact rounds of the milkman's list 

 of calls. Certain streets, certain houses, certain tenements in 

 houses become infected, always in some measure, and in certain 

 instances in a remarkable measure, because they deal with the 

 particular milkman whose milk is implicated. These sections 

 have sometimes been whole villages, at other times a group of 

 houses in a restricted local area, having absolutely nothing in 

 common but the milk supply. On more than one occasion a house 

 at a distance, and altogether out of the district, becomes infected. 

 On inquiry it is found, that by some means or other implicated 

 milk was consumed there. Even in towns the incidence is plain. 

 In the epidemic at Macclesfield in 1889 Dr Parsons found that TJ 

 per cent, of the houses being served with the suspected milk were 

 invaded with illness. In other outbreaks the number of houses 

 served and houses attacked are almost equal 



It is this characteristic of localisation in milk epidemics which 

 affords the primary clue as to causation. It is, of course, in some 

 degree universally present, although it frequently happens that it 

 remains obscure at the time of the outbreak, and is only revealed 

 after much careful inquiry. We might choose illustrations from 

 a number of cases, but we could scarcely select a simpler one than 

 the record of the Wimbledon outbreak of scarlet fever and sore 

 throat at Christmas 1886: — 



